The present invention relates to coated printing papers having good printability, good color print quality and air cleaning effect, especially those on which news ink is used.
Against the background of growing demands for removing harmful substances in daily life such as offensive odors, along with a growing awareness of the need to protect the environment, titanium oxides are drawing attention. Such oxides have been conventionally used as pigments for papermaking on account of their good opacity; and techniques for supporting fine titanium oxides on paper are under development in order to effectively utilize their known ability to induce redox reactions by using light energy to decompose various harmful substances in the atmosphere. For example, a photocatalytic paper internally containing a water-soluble polymer and a photocatalytic material such as a titanium oxide has been disclosed (see patent document 1), but the inclusion of a photocatalytic material within paper layers is neither efficient nor sufficiently effective because it produces its catalytic effect by exposure to light. In order to increase catalytic efficiency, it is thought that a photocatalytic material should be supported as close as possible to a paper surface; or most effectively, paper should be coated with the material. For example, a method has been disclosed by which fine titanium oxide are bonded to an inorganic binder such as colloidal silica and bonded around it by an organic adhesive (see patent document 2). However, such paper is not common and there is limited incentive to use them in view of current environmental awareness. Photocatalytic technologies would be most effectively utilized if they could be applied to e.g., the cover pages of newspapers because currently the most common papers are printing papers, and especially newspapers are published everyday.
Recently, with the growth of various printing technologies there is a growing trend in employing multicolor printing and using printing press with greatly improved printing speed. This tendency is also seen in newspaper printing. Multicolor printing of newsprint paper takes place under conventional printing conditions, i.e. penetration drying type inks are used for printing on conventional newsprint by high-speed coldset rotary presses to meet the need for immediate mass printing typical of newspaper printing and for cost-related reasons. However, when paper is coated by conventional methods, the ink drying properties of the paper are very poor. Therefore, when using penetration drying type inks on such paper printed by high-speed coldset rotary presses, there remains some undried ink which is deposited on guide rolls and transferred to the paper which will cause the final quality to deteriorate.